R12 needs to be replaced with a compatible gas, R12 is a CFC and not good for the environment so not in use anymore. My '94 lude runs R134 as it has been converted, some have been and some have not, you can tell because there will be a shiny sticker near the bonnet release/radiator saying R134a and if you are in any doubt see a speciallist, old R12 and new compatible gasses are designed to run in a particular system and you can't swap them around. You can still have an R12 system converted to R134 but it's expensive and if you can get compatible then there is no reason to unless you have a major leak then replacing the system to take R134 will most likely fix the leak as half the stuff needs to be replaced to do it.
As for the system being "dry" for that abount of time, could be dead, thing to do would be fined a person you can nab an old can of gas from if it's R134 and put some in the system with the ac running, as long as the clutch engages and runs when you add the gas it'll be ok, possibly need new seals but again they may rehydrate enough to keep the gas in or the halfords stuff has a mild leak sealer that will stop minor seal leaks, if you add gas and it all falls out right away stop the AC from running and have the system repaired prefessionally as running a compressor pump dry will kill it for sure. There are a lot of variables but a mate's diesel astra was dry for about 8-12 months and a half can of gas filled it and it ran perfectly for a while until the system sprung a leak and vented all the gas into the car
think it ran for a good few months before giving up but tbh if something is going to go it will go regardless of when you regas the system.Also I miss living that close to St Albans, used to be around the Berkhamsted/Chesham area, so easy to get into London and so many parts places easily within reach, now I live in the bloody sticks and there is nothing around for miles, especially misc items like bolts, trim clips, pattern parts for some things etc. Closest places are Halfords or Halfords Auto Centre type places. No allparts, eurocarparts, nowt, depressing when all you need is one tiny generic part but everywhere is closed or like halfords about 10 miles away
